Ore slurry pre-treatment method and ore slurry manufacturing method

ABSTRACT

Provided is a hydrometallurgical process for nickel oxide ore effectively reducing the amount of sulfuric acid used in the leaching step and the amount of a neutralizer such as slaked lime used in the final neutralization step without reducing nickel yield. The present invention is a method for pre-treating ore slurry to be submitted for leaching treatment in a hydrometallurgical process for nickel oxide ore, the method comprising: a separating step for separating the ore slurry into a coarse particle fraction, in which particles having a particle diameter of less than 45 μm are 30 mass % of the solids or less, and a fine particle fraction, and feeding said fine particle fraction to the leaching process; and a vibration sieving step for separating the separated coarse particle fraction into oversize particles and undersize particles using vibration sieving and feeding the ore slurry of said undersize particles to the leaching process.

TECHNICAL FIELD

The present invention relates to a method for pre-treating ore slurry,and more particularly to a method for pre-treating ore slurry to beprovided to a leaching treatment in a hydrometallurgical process fornickel oxide ore and a method for manufacturing ore slurry to beprovided to the leaching treatment.

BACKGROUND ART

In recent years, a high pressure acid leaching method using sulfuricacid has been gathering attention as a hydrometallurgical process fornickel oxide ore. This method is different from a dry smelting methodthat is a general smelting method for a nickel oxide ore of the relatedart and includes a continuous wet step without including dry steps suchas reducing and drying steps. Thus, the method is advantageous in regardto energy and cost. In addition, the method is also advantageous in thatit is possible to obtain a sulfide containing nickel (hereinafter, alsoreferred to as “nickel sulfide”), whose nickel grade is improved toabout 50% by mass (hereinafter, “% by mass” is simply referred to as“%”). The nickel sulfide is precipitated and generated through processesin which, after washing a leachate obtained by leaching the nickel oxideore, by blowing a hydrogen sulfide gas thereto, a sulfuration reactionis caused to occur (a sulfuration step).

In a step for leaching metal from the nickel oxide ore by such a hightemperature pressure acid leaching method (hereinafter, also simplyreferred to as “leaching step”), since impurity elements such as iron,magnesium, manganese, and aluminum are leached by sulfuric acid inaddition to nickel and cobalt as recovery targets, an excessive amountof sulfuric acid is necessary for the treatment.

Further, in the sulfuration step for recovering nickel and cobalt,nickel and cobalt are selectively recovered as sulfides, but most of theimpurity elements such as iron, magnesium, manganese, and aluminumleached by the leaching treatment in a leaching step do not formsulfides and remain in a barren solution obtained after sulfides areseparated. In order to discharge this barren solution, it is necessaryin a final neutralization step that metal ions remaining in the barrensolution are precipitated and removed by a neutralization treatment.

Herein, in the final neutralization step, a method is generallyperformed in which the pH of the barren solution is increased to about 5by adding a limestone slurry to the barren solution obtained through thesulfuration step so as to remove iron and aluminum and then the pH isincreased to about 9 by adding a slaked lime slurry thereto so as toremove magnesium and manganese. Therefore, since the necessary amount(added amount) of the slaked lime slurry is determined depending on theamounts of magnesium ions and manganese ions remaining in the barrensolution, a large amount of slaked lime slurry is needed in a case wherethe content of magnesium and the content of manganese in the nickeloxide ore are large.

Patent Document 1 discloses a technique of providing a simple and highlyefficient smelting method as the entire process by simplification of aleaching step and a solid-liquid separation step, reducing the amount ofneutralizer consumed in a neutralization step and the amount of aprecipitate, an efficient method of repeatedly using water, and the likein a hydrometallurgical process for recovering nickel from a nickeloxide ore on the basis of high temperature pressure leaching. However,Patent Document 1 does not disclose the technical idea for reducing theamount of sulfuric acid used in the leaching treatment in the leachingstep or reducing the amount of slaked lime used in the aforementionedfinal neutralization step.

Patent Document 1: Japanese Unexamined Patent Application, PublicationNo. 2005-350766

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention is proposed in view of the circumstances asdescribed above, and an object thereof is to provide a method capable ofeffectively reducing the amount of sulfuric acid used in a leaching stepand the amount of neutralizer such as slaked lime used in a finalneutralization step in a hydrometallurgical process for nickel oxide orewithout reducing nickel yield.

Means for Solving the Problems

The present inventors have conducted intensive studies to solve theaforementioned problems. As a result, the present inventors have foundthat by carrying out a specific pre-treatment on ore slurry to beprovided to a leaching treatment in a leaching step of ahydrometallurgical process for nickel oxide ore, the amount of agentssuch as sulfuric acid and slaked lime used in a smelting process can bereduced without reducing nickel yield, and thus the present inventionhas been completed. That is, the present invention provides thefollowing.

(1) A first invention of the present invention is a method forpre-treating ore slurry to be provided to a leaching treatment in ahydrometallurgical process for nickel oxide ore, the method including: aseparation step for separating ore slurry into a coarse particlefraction in which particles having a particle diameter of less than 45μm are 30% by mass or less in a solid content and a fine particlefraction and supplying the fine particle fraction to the leachingtreatment; and a vibration sieving step for separating, by a vibrationsieve, the separated coarse particle fraction into a fraction on thesieve and a fraction under the sieve and supplying the fraction underthe sieve as ore slurry to the leaching treatment.

(2) A second invention of the present invention is the method forpre-treating ore slurry in the first invention, in which a mesh size ofthe vibration sieve is 300 μm or more.

(3) A third invention of the present invention is the method forpre-treating ore slurry in the first or second invention, in which anyone or more of a hydrocyclone and a density separator are used in theseparation step.

(4) A fourth invention of the present invention is the method forpre-treating ore slurry in any one of the first to third inventions, inwhich the separation step includes a classification and separation stepfor supplying the ore slurry to a hydrocyclone and subjecting the oreslurry to classification and separation, and a specific gravityseparation step for supplying an underflow classified by thehydrocyclone in the classification and separation step to a densityseparator and subjecting the underflow to specific gravity separation.

(5) A fifth invention of the present invention is the method forpre-treating ore slurry in any one of the first to fourth inventions, inwhich the hydrometallurgical process for nickel oxide ore includes oreslurry formation step for forming slurry of the nickel oxide ore (oreslurry), a leaching step for carrying out a leaching treatment on theore slurry under high temperature and high pressure by adding sulfuricacid, a solid-liquid separation step for separating a residue while theobtained leached slurry is washed in multiple stages, to obtain aleachate containing nickel and impurity elements, a neutralization stepfor separating a neutralized precipitate containing the impurityelements by adjusting a pH of the leachate to obtain apost-neutralization solution containing nickel, a sulfuration step forcarrying out a sulfuration treatment on the post-neutralization solutionto generate a sulfide containing nickel and a barren solution, and afinal neutralization step for recovering and detoxifying the barrensolution discharged in the sulfuration step.

(6) A sixth invention of the present invention is a method formanufacturing ore slurry to be provided to a leaching treatment in ahydrometallurgical process for nickel oxide ore, the method including:ore slurry formation step for obtaining a coarse ore slurry from thenickel oxide ore; a separation step for separating the coarse ore slurryinto a coarse particle fraction in which particles having a particlediameter of less than 45 μm are 30% by mass or less in a solid contentand a fine particle fraction; a vibration sieving step for separating,by a vibration sieve, the separated coarse particle fraction into afraction on the sieve and a fraction under the sieve; and ore slurrycondensation step for loading the ore slurry of the fine particlefraction separated in the separation step and the ore slurry of thefraction under the sieve separated in the vibration sieving step into asolid-liquid separation device and separating and removing moisturecontained in the ore slurry to condense ore components.

Effects of the Invention

According to the present invention, it is possible to effectively reducethe amount of sulfuric acid used in the leaching step and the amount ofa neutralizer such as slaked lime used in the final neutralization stepin the hydrometallurgical process for nickel oxide ore without reducingnickel yield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process diagram illustrating an example of the flow of ahydrometallurgical process for nickel oxide ore.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a specific embodiment of the present invention(hereinafter, referred to as “the present embodiment”) will be describedin detail. Incidentally, the present invention is not limited to thefollowing embodiment, and various modifications can be made within therange that does not change the spirit of the present invention.

«1. Method for Pre-Treating Ore Slurry»

The method for pre-treating ore slurry according to the presentembodiment is a method for pre-treating slurry of a nickel oxide ore tobe provided to a leaching treatment, for example, by high temperaturehigh pressure acid leaching in a hydrometallurgical process for nickeloxide ore. Specifically, the method includes: a separation step forseparating ore slurry of a nickel oxide ore into a coarse particlefraction in which particles having a particle diameter of less than 45μm are 30% by mass or less in a solid content and a fine particlefraction and supplying the fine particle fraction to the leachingtreatment; and a vibration sieving step for separating, by a vibrationsieve, the separated coarse particle fraction into a fraction on thesieve and a fraction under the sieve and supplying the ore slurry of thefraction under the sieve to the leaching treatment.

Herein, it is known that in the hydrometallurgical process for nickeloxide ore, the amount of sulfuric acid used in the leaching treatment ofa leaching step and the amount of a neutralizer such as slaked lime usedin a neutralization treatment of a final neutralization step areincreased by the presence of elements such as iron, magnesium,manganese, and aluminum which are metal elements other than nickel andcobalt contained in the nickel oxide ore serving as a raw material ore.Such metal elements are mixed, mainly as gangue components, in theslurry of the nickel oxide ore (ore slurry) to be provided to theleaching treatment. The present inventors found that the ganguecomponents exist as coarse particles in the ore slurry, for example,coarse particles having a particle diameter of 45 μm or more.

In this regard, low nickel-containing particles in the ore slurry to beprovided to the leaching treatment in the leaching step, that is, coarseparticle ore is separated and further subjected to a pre-treatment toremove the coarse particle ore by a vibration sieve. Therefore, theamount of sulfuric acid used in the leaching step and the amount ofslaked lime used in the final neutralization step can be effectivelyreduced.

<1-1. Separation Step>

In the separation step, the ore slurry of the nickel oxide ore isseparated into a “coarse particle fraction” in which particles having aparticle diameter of less than 45 μm are 30% by mass or less in a solidcontent and a “fine particle fraction.” The fine particle fractionobtained by separation becomes ore slurry to be supplied to the leachingtreatment without any change.

In the separation step, by using a classification and separationfacility or a specific gravity separation facility and determining theoperation condition thereof, it is possible to separate the ore slurryinto a coarse particle fraction in which the percentage of particleshaving a particle diameter of less than 45 μm in the ore slurry is 30%by mass or less and a fine particle fraction.

Herein, when the percentage of particles having a particle diameter ofless than 45 μm of the coarse particle fraction in the ore slurry to beprovided to the vibration sieving step of the subsequent step to bedescribed later is more than 30% by mass, the particles having aparticle diameter of less than 45 μm adhere to the low nickel-containingcoarse particles and thus the particles having a particle diameter ofless than 45 μm are removed, together with the low nickel-containingparticles, on the vibration sieve. On the other hand, although thepercentage of particles having a particle diameter of less than 45 μm ofthe coarse particle fraction in the ore slurry to be supplied to thevibration sieve is desirably near 0%, when the percentage of particleshaving a particle diameter of less than 45 μm is decreased, the lownickel-containing coarse particles are mixed with the fine particlefraction separated from the coarse particle fraction. For example, whenthe percentage of particles having a particle diameter of less than 45μm is less than 10% by mass, the low nickel-containing coarse particlesstart to be mixed with the fine particle fraction.

In the separation treatment in the separation step, it is preferable toperform the separation treatment using any one or more of a hydrocycloneand a density separator. In the separation treatment using ahydrocyclone or a density separator, the ore slurry can be separatedinto an underflow and an overflow with high accuracy on the basis of theparticle size, which is preferable.

In addition, this separation step more preferably includes aclassification and separation step for supplying the ore slurry to ahydrocyclone and subjecting the ore slurry to classification andseparation and a specific gravity separation step for supplying anunderflow classified by the hydrocyclone in the classification andseparation step to a density separator and subjecting the underflow tospecific gravity separation.

That is, the amount of the nickel oxide ore (ore slurry) to be treatedin the hydrometallurgical process is large, and the particles of the oreslurry are, for example, fine particles in which 80% to 95% of theparticles have a particle diameter of less than 45 μm. For this reason,it is preferable to first carry out a classification and separationtreatment using a hydrocyclone that is suitable for treating a largeamount of the ore slurry and suitable for treating the fine particlefraction, that is, treatment in a case where distribution to theoverflow is large.

Subsequently, it is preferable to carry out a specific gravityseparation treatment using a density separator that is suitable fortreatment in a case where the treated amount is relatively small and thedistribution ratios of the underflow and the overflow are almost thesame, to the ore slurry whose amount to be treated is largely reduced.

In this way, by performing the separation treatment by theclassification and separation treatment using a hydrocyclone and thespecific gravity separation treatment using a density separator in theseparation step, coarse particles containing gangue components in theore slurry, that is, low nickel-containing particles can be efficientlyseparated and removed.

<1-2. Vibration Sieving Step>

Next, the ore slurry of the coarse particle fraction which is separatedin the separation step and in which particles having a particle diameterof less than 45 μm are 30% by mass or less in a solid content isseparated, by using a vibration sieve, into a fraction on the sieve anda fraction under the sieve and the ore slurry of the fraction under thesieve is supplied to the leaching treatment in the leaching step. Inthis way, by carrying out the treatment by the vibration sieve, the oreparticles having a low nickel grade are separated and the ore particlescan be dehydrated. Thus, a dehydration step or the like is notseparately provided and the ore particles can be deposited without anychange.

The mesh size of the vibration sieve to be used in a vibration sievingtreatment is not particularly limited, but is desirably set to about 300μm to 500 μm. When the mesh size of the vibration sieve is less than 300μm, the percentage of ore particles remaining on the sieve is increased,and in accordance with this increase, fine particles having a highnickel content which adhere to the ore particles and remain on the sievemay be increased. On the other hand, when the mesh size of the vibrationsieve is more than 500 μm, the ore particles having a low nickel gradeare mixed with the fraction under the sieve in some cases.

As described above, the method for pre-treating ore slurry according tothe present embodiment includes a separation step for separating oreslurry to be provided to a leaching treatment in a hydrometallurgicalprocess for nickel oxide ore into a coarse particle fraction in whichparticles having a particle diameter of less than 45 μm are 30% by massor less in a solid content and a fine particle fraction and a vibrationsieving step for performing a sieving treatment on the separated coarseparticle fraction by a vibration sieve. According to this, in thefraction on the vibration sieve obtained through the vibration sievingstep, gangue components such as iron, magnesium, manganese, and aluminumcan be efficiently separated. Then, by supplying other separatedcomponents, that is, the fine particle fraction separated in theseparation step and the component of the fraction under the vibrationsieve as the ore slurry to the leaching treatment, the amount ofsulfuric acid used in the leaching step and the amount of a neutralizersuch as slaked lime used in the final neutralization step in thehydrometallurgical process can be effectively reduced.

Hereinafter, the hydrometallurgical process for nickel oxide ore towhich the method for pre-treating ore slurry is applied will bedescribed in detail.

«2. Regarding Hydrometallurgical Process for Nickel Oxide Ore»

The hydrometallurgical process for nickel oxide ore is, for example, asmelting process for leaching nickel to recover nickel from the nickeloxide ore by using a high pressure acid leaching method (HPAL method).

FIG. 1 is a process diagram illustrating an example of the flow of ahydrometallurgical process for nickel oxide ore by a high pressure acidleaching method. As illustrated in the process diagram of FIG. 1, thehydrometallurgical process for nickel oxide ore includes: ore slurryformation step S1 for forming the nickel oxide ore as slurry; ore slurrycondensation step S3 for condensing ore components by removing moisturecontained in the ore slurry; a leaching step S4 for preforming aleaching treatment under high temperature and high pressure by addingsulfuric acid to the produced ore slurry; a solid-liquid separation stepS5 for separating a residue while the obtained leached slurry is washedin multiple stages to obtain a leachate containing nickel and impurityelements; a neutralization step S6 for separating a neutralizedprecipitate containing impurity elements by adjusting the pH of theleachate to obtain a post-neutralization solution containing nickel; anda sulfuration step S7 for generating a sulfide containing nickel (nickelsulfide) by adding a sulfurizing agent to the post-neutralizationsolution. Furthermore, this hydrometallurgical process includes a finalneutralization step S8 for recovering and detoxifying the leachingresidue separated in the solid-liquid separation step S5 and a barrensolution discharged in the sulfuration step S7.

Further, in the present embodiment, it is characterized in that beforecarrying out the leaching treatment using sulfuric acid on the oreslurry, a pre-treatment step S2 for pre-treating the slurried ore isprovided.

(1) Ore Slurry Formation Step

In the ore slurry formation step S1, the nickel oxide ore serving as araw material ore is classified at a predetermined classifying point sothat oversized ore particles are removed, and then water is added toundersized ore particles to obtain a coarse ore slurry.

Herein, the nickel oxide ore serving as a raw material ore is orecontaining nickel and cobalt, and a so-called laterite ore such as alimonite ore and a saprolite ore is mainly used. The content of nickelin the laterite ore is typically 0.8% by weight to 2.5% by weight andnickel is contained as hydroxide or silica-magnesia (magnesium silicate)mineral. Further, the content of iron is 10% by weight to 50% by weightand iron is mainly in the form of trivalent hydroxide (goethite);however, some divalent iron is contained in silica-magnesia mineral.Further, in addition to such a laterite ore, an oxide ore containingvaluable metals such as nickel, cobalt, manganese, and copper, forexample, manganese nodules existing at the bottom of the deep part ofthe sea, or the like are used.

The method for classifying the nickel oxide ore is not particularlylimited as long as it can classify ores on the basis of a desiredparticle diameter, and for example, the classification can be performedby sieve classification using a general grizzly sieve, a vibrationsieve, or the like. Further, the classifying point is not particularlylimited, and a classifying point for obtaining ore slurry composed ofore particles having a desired particle diameter value or less can beappropriately set.

(2) Pre-Treatment Step

In the present embodiment, before carrying out the leaching treatment onthe ore slurry, the pre-treatment step S2 for pre-treating the oreslurry obtained through the ore slurry formation step is provided.

The pre-treatment step S2 includes a separation step S21 for separatingthe ore slurry obtained through the ore slurry formation step S1 into acoarse particle fraction in which particles having a particle diameterof less than 45 μm are 30% by mass or less in a solid content and a fineparticle fraction and then supplying the fine particle fraction to theleaching treatment in the leaching step S4 described later and avibration sieving step S22 for separating, by a vibration sieve, theseparated coarse particle fraction into a fraction on the sieve and afraction under the sieve and then supplying the ore slurry of thefraction under the sieve to the leaching treatment in the leaching stepS4.

A detailed description of the pre-treatment in the pre-treatment step S2is not provided herein since the pre-treatment is the same as describedabove, but by carrying out the pre-treatment on the ore slurry in thisway, it is possible to separate gangue components such as iron,magnesium, manganese, and aluminum from the ore slurry and toeffectively reduce the amount of sulfuric acid used in the leaching stepand the amount of a neutralizer such as slaked lime used in the finalneutralization step without reducing nickel yield.

The ore slurry containing the fine particle fraction separated in theseparation step S21 in the pre-treatment step S2 and the ore slurryclassified into the fraction under the sieve in the vibration sievingstep S22 are supplied to the leaching treatment in the leaching step S4through the ore slurry condensation step S3 described below.

(3) Ore Slurry Condensation Step

In the ore slurry condensation step S3, the ore slurry containing thefine particle fraction separated in the separation step S21 in theaforementioned pre-treatment step S2 and the ore slurry containing oreparticles of the fraction under the sieve separated in the vibrationsieving step S22 are loaded into a solid-liquid separation device andmoisture contained in the coarse ore slurry is separated and removed tocondense ore components, thereby obtaining the ore slurry.

Specifically, in the ore slurry condensation step S3, each ore slurry isloaded, for example, into a solid-liquid separation device such as athickener, and the solid components are precipitated and extracted fromthe lower portion of the device, while moisture forming a supernatant isoverflowed from the upper portion of the device; thus, solid-liquidseparation is carried out. Through this solid-liquid separationtreatment, the moisture in the ore slurry is reduced, and the orecomponents in the slurry are condensed so that ore slurry having, forexample, a solid concentration of about 40% by weight is obtained.

Incidentally, as described above, by undergoing the ore slurry formationstep S1, the pre-treatment step S2 including the separation step S21 andthe vibration sieving step S22, and the ore slurry condensation step S3,it is possible to manufacture ore slurry to be provided to the leachingtreatment in the leaching step S4 described below and the methodincluding these steps can be defined as a method for manufacturing oreslurry.

(4) Leaching Step

In the leaching step S4, the leaching treatment, for example, using ahigh pressure acid leaching method is carried out on the produced oreslurry. Specifically, sulfuric acid is added to the ore slurrycontaining the nickel oxide ore serving as raw material and the oreslurry is stirred while being pressurized under a high temperaturecondition of 220° C. to 280° C., thereby generating a leached slurrycomposed of a leachate and a leaching residue.

In the leaching treatment in the leaching step S4, a leaching reactionrepresented by the following formulae (i) to (iii) and a hightemperature thermal hydrolysis reaction represented by the followingformulae (iv) and (v) occur so that leaching of nickel, cobalt, and thelike as sulfates and fixation of the leached iron sulfate as hematiteare performed.

-   -   Leaching Reaction        MO+H₂SO₄        MSO₄+H₂O  (i)        (incidentally, M in the formula represents Ni, Co, Fe, Zn, Cu,        Mg, Cr, Mn, or the like)        2Fe(OH)₃+3H₂SO₄        Fe₂(SO₄)₃+6H₂O  (ii)        FeO+H₂SO₄→FeSO₄+H₂O  (iii)    -   High Temperature Thermal Hydrolysis Reaction        2FeSO₄+H₂SO₄+½O₂        Fe₂(SO₄)₃+H₂O  (iv)        Fe₂(SO₄)₃+3H₂O        Fe₂O₃+3H₂SO₄  (v)

Herein, conventionally, an excessive amount is generally used as theamount of sulfuric acid added in the leaching step S4. Since impuritiessuch as iron, magnesium, manganese, and aluminum are contained in thenickel oxide ore in addition to nickel and cobalt and these impuritiesare also leached by sulfuric acid, in order to increase a yield of arecovery target such as nickel or cobalt, the leaching treatment isperformed by adding an excessive amount of sulfuric acid. On the otherhand, in the present embodiment, a specific pre-treatment is carried outin the aforementioned pre-treatment step S2 on the ore slurry to beprovided to the leaching treatment in the leaching step S4 so that theconcentration of impurities contained in the ore slurry can bedecreased, and the added amount of sulfuric acid used in the leachingtreatment can be effectively reduced.

(5) Solid-Liquid Separation Step

In the solid-liquid separation step S5, the leached slurry is separatedinto a leachate containing impurity elements in addition to nickel andcobalt and a leaching residue while the leached slurry obtained throughthe leaching step S4 is washed in multiple stages.

In the solid-liquid separation step S5, for example, the leached slurryis mixed with a rinsing liquid and then subjected to the solid-liquidseparation treatment by a solid-liquid separation facility such as athickener. Specifically, first, the leached slurry is diluted with therinsing liquid, and then the leaching residue in the slurry is condensedas a precipitate in the thickener. According to this, the remainingnickel adhered to the leaching residue can be decreased depending on thedegree of dilution. Incidentally, the solid-liquid separation treatmentmay be performed, for example, by adding an anionic flocculant.

In the solid-liquid separation step S5, it is preferable that thesolid-liquid separation be carried out while the leached slurry iswashed in multiple stages. As a multiple washing method, for example, acontinuous countercurrent multi-stage washing method in which theleached slurry is brought into countercurrent contact with a rinsingliquid can be used. According to this, the rinsing liquid to be newlyintroduced into the system can be reduced and the recovery rate ofnickel and cobalt can be improved to 95% or more. In addition, therinsing liquid (rinsing water) is not particularly limited, but it ispreferable to use a liquid which contains no nickel and has no effect onthe step. For example, as the rinsing liquid, preferably, a barrensolution to be obtained in the sulfuration step S7 of the subsequentsteps can be repeatedly used.

(6) Neutralization Step

In the neutralization step S6, the pH of the leachate separated in thesolid-liquid separation step S5 is adjusted and a neutralizedprecipitate containing impurity elements is separated to thereby obtaina post-neutralization solution containing nickel and cobalt.

Specifically, in the neutralization step S6, a neutralizer such ascalcium carbonate is added to the leachate while the oxidation of theseparated leachate is suppressed such that the pH of thepost-neutralization solution to be obtained is adjusted to 4 or less,preferably to 3.0 to 3.5, and more preferably to 3.1 to 3.2, therebygenerating a post-neutralization solution and a neutralized precipitateslurry containing trivalent iron, aluminum, and the like as impurityelements. In the neutralization step S6, the impurities are removed asthe neutralized precipitate in this way and a post-neutralizationsolution serving as a mother liquor for recovering nickel is generated.

(7) Sulfuration Step

In the sulfuration step S7, a sulfurizing agent such as hydrogen sulfidegas is blown into the post-neutralization solution serving as a motherliquor for recovering nickel to cause a sulfuration reaction to occur,thereby generating a sulfide containing nickel (and cobalt)(hereinafter, also simply referred to as “nickel sulfide”) and a barrensolution.

The post-neutralization solution serving as a mother liquor forrecovering nickel is a sulfuric acid solution in which the impuritycomponents in the leachate are decreased through the neutralization stepS6. Incidentally, there is a possibility that about several g/L of iron,magnesium, manganese, and the like are contained as impurity componentsin the mother liquor for recovering nickel, but these impuritycomponents have low stability as a sulfide (as compared to nickel andcobalt to be recovered) and are not contained in the nickel sulfide tobe generated.

The sulfuration treatment in the sulfuration step S7 is executed in anickel recovery facility. The nickel recovery facility includes, forexample, a sulfuration reaction tank in which a sulfuration reaction isperformed by blowing hydrogen sulfide gas or the like into thepost-neutralization solution serving as the mother liquor and asolid-liquid separation tank in which nickel sulfide is separated andrecovered from the post-sulfuration reaction solution. The solid-liquidseparation tank is configured, for example, by a thickener or the like,and the nickel sulfide that is a precipitate is separated and recoveredfrom the bottom portion of the thickener by carrying out a sedimentationand separation treatment on the slurry containing nickel sulfide andobtained after the sulfuration reaction. Meanwhile, the aqueous solutioncomponents are overflowed and recovered as a barren solution.Incidentally, the recovered barren solution is a solution having anextremely low concentration of valuable metals such as nickel andcontains impurity elements such as iron, magnesium, and manganeseremaining without being sulfurized. This barren solution is transferredto the final neutralization step S8 described below and subjected to adetoxification treatment.

(8) Final Neutralization Step

In the final neutralization step S8, a neutralization treatment (adetoxification treatment) to adjust the pH to a predetermined pH rangesatisfying the discharge standard is carried out on the barren solutiondischarged in the aforementioned sulfuration step S7 which containsimpurity elements such as iron, magnesium, and manganese. In this finalneutralization step S8, it is possible to treat the leaching residuedischarged from the solid-liquid separation treatment in thesolid-liquid separation step S5 together with the barren solution.

A method for the detoxification treatment in the final neutralizationstep S8, that is, a method for adjusting the pH is not particularlylimited, but for example, the pH can be adjusted to a predeterminedrange by adding a neutralizer such as a calcium carbonate (limestone)slurry or a calcium hydroxide (slaked lime) slurry.

In the final neutralization treatment in the final neutralization stepS8, it is possible to perform a stepwise neutralization treatmentincluding a neutralization treatment at the first stage (first finalneutralization step S81) using limestone as a neutralizer and aneutralization treatment at the second stage (second finalneutralization step S82) using slaked lime as a neutralizer. Byperforming the stepwise neutralization treatment in this way, theneutralization treatment can be performed efficiently and effectively.

Specifically, in the first final neutralization step S81, the barrensolution discharged and recovered from the sulfuration step S7 and theleaching residue separated in the solid-liquid separation step S5 areloaded into a neutralization treatment tank and subjected to a stirringtreatment by adding a limestone slurry. In this first finalneutralization step S81, by adding the limestone slurry, the pH of asolution to be treated such as the barren solution is adjusted to 4 to5.

Next, in the second final neutralization step S82, the stirringtreatment is carried out on the solution subjected to the neutralizationtreatment at the first stage by adding a limestone slurry, by adding aslaked lime slurry. In this second final neutralization step S82, byadding the slaked lime slurry, the pH of the solution to be treated isincreased to 8 to 9.

By performing such a two-stage neutralization treatment, aneutralization treatment residue is generated and stored in a tailingsdam (a tailings residue). Meanwhile, a solution obtained after theneutralization treatment satisfies the discharge standard and isdischarged to the outside of the system.

Herein, in the treatment in the final neutralization step, the amount ofa neutralizer such as slaked lime is determined according to the amountof impurity element ions such as magnesium ions and manganese ionsremaining in the barren solution. In the present embodiment, a specificpre-treatment is carried out in the aforementioned pre-treatment step S2on the ore slurry to be provided to the leaching treatment in theleaching step S4 so that the impurity elements such as magnesium andmanganese contained in the ore slurry can be reduced. According to this,it is possible to decrease the concentration of these elements containedin the barren solution and effectively reduce the amount of aneutralizer used in the neutralization treatment in the finalneutralization step.

EXAMPLES

Hereinafter, the present invention will be described in more detail bymeans of Examples, but the present invention is not limited to thefollowing Examples at all.

Example 1

A hydrometallurgical treatment for nickel oxide ore formed from theprocess diagram illustrated in FIG. 1 was performed in the followingmanner. That is, first, as a pre-treatment step for ore slurry, oreslurry obtained by slurrying a nickel oxide ore having a compositionpresented in the following Table 1 was supplied to a hydrocyclone(manufactured by Salter Cyclones Ltd., SC1030-P type) to be subjected toa classification and separation treatment and then the underflowdischarged from the hydrocyclone was supplied to a density separator(manufactured by CFS Co., Ltd., 6×6 type) to be subjected to a specificgravity separation treatment. By these separation treatments, ore slurry(coarse particle fraction) in which the content of particles having aparticle diameter of less than 45 μm in the underflow solid content ofthe density separator is 25% by mass was obtained.

TABLE 1 Ni [%] Mg [%] Solid [t/h] <45 μm [%] Nickel oxide ore 0.91 1.5960 89

Next, the obtained ore slurry was supplied at a solid concentration of20% to a vibration sieve equipped with a sieve having a mesh size of 300μm (manufactured by Sizetech, VDS27-6 type) to be subjected to avibration sieving treatment. With this vibration sieve, solid contentshaving a nickel grade of 0.83% and a magnesium grade of 7.50%, that is,low nickel-containing particles were obtained as a fraction on thesieve. Meanwhile, the ore slurry of the fraction under the vibrationsieve and the ore slurry of the fine particle fraction obtained in theaforementioned separation step were supplied to the leaching step inwhich the leaching treatment is carried out on the ore.

At this time, the nickel loss rate to the fraction on the vibrationsieve was 6.7%. In addition, the amount of sulfuric acid consumed in theleaching treatment in the leaching step to which the ore slurry wassupplied was 272 kg/ore tonne. Further, when the sulfuration treatmentwas carried out on the leachate obtained through the leaching treatment(the sulfuration step) and the final neutralization treatment wascarried out on the barren solution obtained by the sulfuration treatment(the final neutralization step), the amount of slaked lime used in theneutralization treatment was 36 kg/ore tonne.

Example 2

By performing a similar operation to Example 1, ore slurry (coarseparticle fraction) in which the content of particles having a particlediameter of less than 45 μm in the underflow solid content of thedensity separator is 30% by mass was obtained. Then, the obtained oreslurry was supplied at a solid concentration of 20% to a vibration sieveequipped with a sieve having a mesh size of 300 μm to be subjected to avibration sieving treatment. With this vibration sieve, solid contentshaving a nickel grade of 0.84% and a magnesium grade of 7.39%, that is,low nickel-containing particles were obtained as a fraction on thesieve. Meanwhile, the ore slurry of the fraction under the vibrationsieve and the ore slurry of the fine particle fraction obtained in theseparation step were supplied to the leaching step in which the leachingtreatment is carried out on the ore.

At this time, the nickel loss rate to the fraction on the vibrationsieve was 6.8%. In addition, the amount of sulfuric acid consumed in theleaching treatment in the leaching step to which the ore slurry wassupplied was 272 kg/ore tonne. Further, when the sulfuration treatmentwas carried out on the leachate obtained through the leaching treatment(the sulfuration step) and the final neutralization treatment wascarried out on the barren solution obtained by the sulfuration treatment(the final neutralization step), the amount of slaked lime used in theneutralization treatment was 36 kg/ore tonne.

Comparative Example 1

By performing a similar operation to Example 1, ore slurry (coarseparticle fraction) in which the content of particles having a particlediameter of less than 45 μm in the underflow solid content of thedensity separator is 35% by mass was obtained. Then, the obtained oreslurry was supplied at a solid concentration of 20% to a vibration sieveequipped with a sieve having a mesh size of 300 μm to be subjected to avibration sieving treatment. With this vibration sieve, solid contentshaving a nickel grade of 0.84% and a magnesium grade of 6.95% wereobtained as the fraction on the sieve. Meanwhile, the ore slurry of thefraction under the vibration sieve and the ore slurry of the fineparticle fraction obtained in the separation step were supplied to theleaching step in which the leaching treatment is carried out on the ore.

At this time, the nickel loss rate to the fraction on the vibrationsieve was 7.7% and was increased as compared to Examples 1 and 2. Thereason for this is considered that since the content of particles havinga particle diameter of less than 45 μm in the ore slurry supplied to thevibration sieve was large, the particles were removed on the sievetogether with the low nickel-containing particles. Incidentally, theamount of sulfuric acid consumed in the leaching treatment in theleaching step to which the ore slurry was supplied was 271 kg/ore tonne.Further, when the sulfuration treatment was carried out on the leachateobtained through the leaching treatment (the sulfuration step) and thefinal neutralization treatment was carried out on the barren solutionobtained by the sulfuration treatment (the final neutralization step),the amount of slaked lime used in the neutralization treatment was 35.5kg/ore tonne.

As described above, in Comparative Example 1, the amount of sulfuricacid used in the leaching step and the amount of slaked lime used in thefinal neutralization step could be reduced, but the nickel yield wasdecreased.

Comparative Example 2

A nickel oxide ore having a composition presented in Table 1 wasslurried and the ore slurry was supplied at a solid concentration of 20%to a vibration sieve equipped with a sieve having a mesh size of 300 μmto be subjected to the vibration sieving treatment, without carrying outthe separation treatment (the specific gravity separation) on the oreslurry. The content of particles having a particle diameter of less than45 μm in the solid content supplied at this time was 80%. With thisvibration sieve, solid contents having a nickel grade of 0.88% and amagnesium grade of 3.95% were obtained as the fraction on the sieve.Meanwhile, the ore slurry of the fraction under the vibration sieve andthe ore slurry of the fine particle fraction obtained in the separationstep were supplied to the leaching step in which the leaching treatmentis carried out on the ore.

At this time, the nickel loss rate to the fraction on the vibrationsieve was 16.9%, which was extremely large. The reason for this isconsidered, similarly to Comparative Example 2, that the content ofparticles having a particle diameter of less than 45 μm in the oreslurry supplied to the vibration sieve was extremely large.Incidentally, the amount of sulfuric acid consumed in the leachingtreatment in the leaching step to which the ore slurry was supplied was270 kg/ore tonne. Further, when the sulfuration treatment was carriedout on the leachate obtained through the leaching treatment (thesulfuration step) and the final neutralization treatment was carried outon the barren solution obtained by the sulfuration treatment (the finalneutralization step), the amount of slaked lime used in theneutralization treatment was 35.0 kg/ore tonne.

As described above, in Comparative Example 2, the amount of sulfuricacid used in the leaching step and the amount of slaked lime used in thefinal neutralization step could be reduced, but the nickel yield wasdecreased.

Comparative Example 3

A nickel oxide ore having a composition presented in Table 1 wasslurried and the ore slurry was supplied to the leaching step in whichthe leaching treatment is carried out, without carrying out thepre-treatment (the specific gravity separation and the vibration sievingtreatment) on the ore slurry.

The amount of sulfuric acid consumed in the leaching treatment in theleaching step to which the ore slurry was supplied was 287 kg/ore tonne.In addition, when the sulfuration treatment was carried out on theleachate obtained through the leaching treatment (the sulfuration step)and the final neutralization treatment was carried out on the barrensolution obtained by the sulfuration treatment (the final neutralizationstep), the amount of slaked lime used in the neutralization treatmentwas 47.5 kg/ore tonne.

As described above, in Comparative Example 3, the amount of sulfuricacid used in the leaching step and the amount of slaked lime used in thefinal neutralization step were increased, and thus it was not possibleto effectively reduce the used amounts thereof.

In the following Table 2, the grades of nickel and magnesium and thecontent of particles having a particles diameter of less than 45 μm inthe solid content, and the nickel loss rate of the ore slurry suppliedto the vibration sieve and the recovery particles recovered on the sieveby the treatment using the vibration sieve in the operations of Examples1 and 2 and Comparative Examples 1 to 3 are collectively presented.

TABLE 2 Particles (on sieve) Ore slurry supplied to vibration sieverecovered by vibration sieve Ni loss Ni [%] Mg [%] Solid [t/h] <45 μm[%] Ni [%] Mg [%] Solid [t/h] <45 μm [%] rate [%] Example 1 0.85 5.329.2 25.0 0.83 7.50 4.30 1.6 6.7 Example 2 0.85 5.02 9.6 30.0 0.84 7.394.40 3.3 6.8 Comparative 0.86 4.78 10.6 35.0 0.84 6.95 5.00 7.4 7.7Example 1 Comparative 0.9 2.09 34.4 80.0 0.88 3.95 10.5 52.3 16.9Example 2 Comparative — — — — — — — — 0 Example 3

Further, in the following Table 3, the amount of sulfuric acid consumedin the leaching step and the amount of slaked lime consumed in the finalneutralization step in the operations of Examples 1 and 2 andComparative Examples 1 to 3 are collectively presented.

TABLE 3 Consumed Consumed amount Ore slurry supplied amount of slaked toleaching step of sulfuric lime Ni [%] Mg [%] Solid [t/h] acid [kg/Ore t][kg/Ore t] Example 1 0.91 1.13 55.7 272.0 36.0 Example 2 0.91 1.13 55.6272.0 36.0 Comparative 0.91 1.10 55.0 271.0 35.5 Example 1 Comparative0.91 1.08 49.5 270.0 35.0 Example 2 Comparative 0.91 1.59 60.0 287.047.5 Example 3

The invention claimed is:
 1. A method for pre-treating ore slurry to beprovided to a leaching treatment in a hydrometallurgical process fornickel oxide ore, the method comprising: a separation step forseparating ore slurry into a coarse particle fraction in which particleshaving a particle diameter of less than 45 μm are 30% by mass or less ina solid content and a fine particle fraction and supplying the fineparticle fraction to the leaching treatment; and a vibration sievingstep for separating, by a vibration sieve having a mesh size of 300 μmor more and 500 μm or less, the separated coarse particle fraction intoa fraction on the sieve and a fraction under the sieve and supplying thefraction under the sieve as ore slurry to the leaching treatment.
 2. Themethod for pre-treating ore slurry according to claim 1, wherein any oneor more of a hydrocyclone and a density separator are used in theseparation step.
 3. The method for pre-treating ore slurry according toclaim 2, wherein the separation step includes a classification andseparation step for supplying the ore slurry to a hydrocyclone andsubjecting the ore slurry to classification and separation, and aspecific gravity separation step for supplying an underflow classifiedby the hydrocyclone in the classification and separation step to adensity separator and subjecting the underflow to specific gravityseparation.
 4. The method for pre-treating ore slurry according to claim1, wherein the hydrometallurgical process for nickel oxide ore includesore slurry formation step for forming slurry of the nickel oxide ore(ore slurry), a leaching step for carrying out a leaching treatment onthe ore slurry under high temperature and high pressure by addingsulfuric acid, a solid-liquid separation step for separating a residuewhile the obtained leached slurry is washed in multiple stages, toobtain a leachate containing nickel and impurity elements, aneutralization step for separating a neutralized precipitate containingthe impurity elements by adjusting a pH of the leachate to obtain apost-neutralization solution containing nickel, a sulfuration step forcarrying out a sulfuration treatment on the post-neutralization solutionto generate a sulfide containing nickel and a barren solution, and afinal neutralization step for recovering and detoxifying the barrensolution discharged in the sulfuration step.
 5. A method formanufacturing ore slurry to be provided to a leaching treatment in ahydrometallurgical process for nickel oxide ore, the method comprising:ore slurry formation step for obtaining a coarse ore slurry from thenickel oxide ore; a separation step for separating the coarse ore slurryinto a coarse particle fraction in which particles having a particlediameter of less than 45 μm are 30% by mass or less in a solid contentand a fine particle fraction; a vibration sieving step for separating,by a vibration sieve having a mesh size of 300 μm or more and 500 μm orless, the separated coarse particle fraction into a fraction on thesieve and a fraction under the sieve; and ore slurry condensation stepfor loading the ore slurry of the fine particle fraction separated inthe separation step and the ore slurry of the fraction under the sieveseparated in the vibration sieving step into a solid-liquid separationdevice and separating and removing moisture contained in the ore slurryto condense ore components.